How to decrypt Apple Pay Payment Token using .net

This project covers steps 3, and 4 of the Apple documentation about how to decrypt Apple Pay. Showed here: https://developer.apple.com/library/archive/documentation/PassKit/Reference/PaymentTokenJSON/PaymentTokenJSON.html

You will need a few things to make this work:

1. You will need the certificate.p12 (name the .p12 file whatever you want) exported from the mac's Keychain Access

   • There are many web sites showing you how to do this online so I wont cover it here in detail
   • But basically you create a certificate signing request on your mac, and upload it to the Apple developer web site
   • You will download the generated Apple Pay Certificate and install (simply click only) on your mac
   • You will open the Keychain Access and export the .p12 file (I did not add a password when exporting the .p12 for this code)

2. You will use openSSL.exe to create the privateKey.der file needed

   • Download and install OpenSSL - I downloaded it from here (windows version): https://slproweb.com/products/Win32OpenSSL.html
   • I used "Win64 OpenSSL v1.1.0L"
   • run the following commands:
     • This will create a sample.key file
     • openssl pkcs12 -in certificate.p12 -nocerts -nodes -out sample.key
     • This will use the sample.key file and create the privateKey.der file that you need
     • openssl pkcs8 -topk8 -inform PEM -outform DER -in sample.key -out privateKey.der -nocrypt

3. You will need the payment token you are trying to decrypt.

   • This is the object returned by apple in its entirety.

4. Place the files in whatever directories you are want.

   • The sample app is pointing to the c:\temp directory

   static readonly string privateKey = @"C:\temp\privateKey.der";
   static readonly string paymentToken = @"C:\temp\payment.json";
   static readonly string p12FileLocation = @"C:\temp\certificate.p12";

If you have any issues please create a bug so we can help others with the same problem.

Thank you. Happy Coding!